This invention relates to an injection pump utilized to inject molten metal such as aluminum, magnesium, zinc and alloys thereof into the mould of a hot or cold chamber type die cast machine.
For die casting zinc and zinc alloys which have relatively low melting points hot chamber type injection pumps have been used for the most part, whereas for die casting aluminum and alloys thereof cold chamber type die cast machines have generally been used because molten aluminum severely corrodes many types of metals. For this reason, ordinary steel cannot be used for the components of the injection pump which come to contact molten aluminum during operation.
Especially, the cylinder and piston or plunger of the injection pump are used under severe conditions in which they slide against each other at high speeds, high temperatures and under high pressures, so that it is important to construct these components with materials having excellent mechanical and chemical characteristics such as high temperature strength, high temperature hardness, thermal stability, corrosion resistant property, etc.
As is well known in the art, an injection pump for use in a die cast machine is immersed in a bath of molten metal for injecting the same into the mould. In the case of aluminum alloys, the temperature of the molten metal is maintained at a temperature of from 630.degree. C. to 700.degree. C. and the piston of the pump is moved at a speed of from 1 to 5 m/sec. to inject the molten metal under a pressure of from 100 to 300 kg/cm.sup.2, for example.
The cylinder or the lining thereof and the piston of such injection pump have been made of ceramics because of their high corrosion resistance. In the past, it has been tried to use sintered bodies of TiB.sub.2 as the ceramic but such trial has not succeeded commercially, because of their low mechanical strength, heat resistant property and low shock proofness.